Method for making carbon nanotube composite preform

ABSTRACT

A method for making a carbon nanotube composite preform includes following steps. A substrate is provided. Carbon nanotubes are formed on the substrate. The carbon nanotubes and the substrate are placed in a solvent for a predetermined time. The carbon nanotubes and the substrate are drawn from the solvent. The carbon nanotubes and the substrate are dried.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/002,116, filed on Dec. 14, 2007, entitled, “CARBON NANOTUBE COMPOSITEPREFORM AND METHOD FOR MAKING THE SAME,” which claims all benefitsaccruing under 35 U.S.C. §119 from China Patent Application No.200710076745.6 filed on Aug. 31, 2007 in the China Intellectual PropertyOffice. The disclosures of the above-identified applications areincorporated herein by reference.

BACKGROUND

1. Field of the Invention

The invention relates to a preform and method for making the same,particularly, to a carbon nanotube composite preform and a method formaking the same.

2. Discussion of Related Art

Carbon nanotubes (CNT) are a novel carbonaceous material and received agreat deal of interest since the early 1990s. Carbon nanotubes haveinteresting and potentially useful electrical and mechanical properties.Due to these and other properties, it becomes an important applicationdirection for CNTs to be used as fillers in engineering materials.

Nowadays, the method for growing a CNT array on a substrate, such as aglass, silicon, or heat-resistant metal substrate has matured. CNTarrays are in widespread use, such as in field emission tubes,ultra-thin flat panel displays, cathode electrodes, biosensors and soon.

However, naturally occurring gas-filled spaces between CNTs in CNTarrays lead to poor radial properties (such as thermal conductivity) andthus affect the properties of the whole material. So it is beneficial tofill gaps between CNTs in the CNT array with metals or polymer materialsto make a composite material. This ensures the composite material hasimproved radial properties.

Conventionally, the CNT composite material is made by directlyinfiltrating the melting metal or polymer material into the CNT array.Referring to an article by H. Huang entitled “Aligned Carbon NanotubeComposite Films for Thermal Management” (Adv Mater., Vol 17, 2005, p1652), the above-described manufacturing process is reported. However,the gaps between the CNTs in the CNT array are so small that somematerials, such as indium, copper, etc., cannot infiltrate the CNT arraywell.

What is needed, therefore, is a CNT composite preform with filterablegaps between CNTs and a simple, low cost, and short cycle method formaking the described CNT composite preform.

SUMMARY

In one embodiment, a CNT composite preform includes a substrate and aplurality of CNTs formed thereon. Each CNT includes a first end adjacentto the substrate and a second end away from the substrate. Gaps betweenthe second ends of the CNTs are bigger than gaps between the first ends.The method for making the CNT composite preform includes the followingsteps: (a) providing a substrate; (b) forming a plurality of CNTs (e.g.,a CNT array) on the substrate; (c) placing the CNTs and the substrate ina solvent for some time; (d) drawing the CNTs and the substrate from thesolvent; (e) drying the CNTs and the substrate to form a CNT compositepreform.

Other advantages and novel features of the present CNT composite preformand the related method for making the same will become more apparentfrom the following detailed description of present embodiments whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present CNT composite preform and the related methodfor making the same can be better understood with reference to thefollowing drawings. The components in the drawings are not necessarilyto scale, the emphasis instead being placed upon clearly illustratingthe principles of the present CNT composite preform and the relatedmethod for making the same.

FIG. 1 is a flow chart of a method for making a CNT composite preform,in accordance with a first embodiment.

FIG. 2 is a cross-sectional schematic view of the CNT composite preformof FIG. 1.

FIG. 3 shows a Scanning Electron Microscope (SEM) image of the secondends of the CNTs which are away from the substrate, after vacuumtreatment process in oxydol solution, in accordance with the firstembodiment.

FIG. 4 shows a Scanning Electron Microscope (SEM) image of across-sectional surface of the CNT composite preform parallel to the CNTaxis, after vacuum treatment process in oxydol solution, in accordancewith the first embodiment.

FIG. 5 shows a Scanning Electron Microscope (SEM) image of the firstends of the CNTs which are near the substrate, after vacuum treatmentprocess in oxydol solution, in accordance with the first embodiment.

FIG. 6 shows a Scanning Electron Microscope (SEM) image of the secondends of the CNTs after vacuum treatment process in water, in accordancewith a second embodiment.

FIG. 7 shows a Scanning Electron Microscope (SEM) image of the secondends of the CNTs after vacuum treatment process in ethanol solvent, inaccordance with a third embodiment.

FIG. 8 shows a Scanning Electron Microscope (SEM) image of the secondends of the CNTs after ultrasonic vibration treatment process in oxydolsolution, in accordance with a fourth embodiment.

FIG. 9 shows a Scanning Electron Microscope (SEM) image of the secondends of CNTs after being removed from water, in accordance with a fifthembodiment.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate at least one preferred embodiment of the present CNTcomposite preform and the related method for making the same, in atleast one form, and such exemplifications are not to be construed aslimiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe, in detail,embodiments of the carbon nanotube (CNT) composite preform and therelated method for making the same.

Referring to FIG. 1, a method for making a CNT composite preformincludes the following steps: (a) providing a substrate; (b) forming aCNT array on the substrate; (c) placing the CNT array and the substratein a solvent for some time; (d) drawing the CNT array and the substratefrom the solvent; (e) drying the CNT array and the substrate to form aCNT composite preform.

In step (a), the substrate is made of at least one material selectedfrom a group consisting of glass, silicon, metal, and metal oxide. Thesubstrate has at least one surface. In step (b), the CNTs are formed bychemical vapor deposition method or laser ablation method. A diameter ofeach CNT in the CNT array is in the approximate range from 1 to 100nanometers. A length of the CNTs in the CNT array is in the approximaterange from 1 to 500 micrometers. In the embodiments, the maximum heightof the CNT array is about 200 micrometers. The gaps between CNTs in theCNT array are in the approximate range from 1 to 100 nanometers. TheCNTs are single-walled CNT, double-walled CNT, or multi-walled CNT.

Step (c) further includes the substeps of: (c1) supplying a solvent;(c2) placing the solvent in a container; (c3) placing the CNT array andthe substrate in the solvent for some time.

In step (c1), the solvent includes at least one substance selected froma group consisting of water, ethanol and oxydol solution. A massconcentration of the oxydol solution is about 25%. The amount of thesolvent is, usefully, enough to immerse the CNT array therein. In step(c3), the immersion time is in an approximate range from 10 to 60minutes.

Step (c) further includes a substep of vacuum treatment or ultrasonicvibration treatment to evacuate the gas between the CNTs in the CNTarray. In the vacuum treatment process, a water-cycle vacuum pump isused to evacuate the gas. The vacuum treatment process takes about 10˜60minutes. Alternatively, the ultrasonic vibration treatment takes about10˜60 minutes. During the aforementioned processes, the gas between theCNTs in the CNT array migrates to the ends of the CNT array away fromthe substrate and forms gas pockets. As a function of the surfacetension of the gas pockets, the ends of the CNTs away from the substrateare shifted to form honeycomb-shaped gaps. The size of the gaps is inthe approximate range from 2 to 300 micrometers.

In step (e), the drying treatment is conducted in a vacuum drying ovenat about 40° C.˜50° C. to vaporize the solvent in the CNT array. Thedrying time is in the approximate range from 10 to 60 minutes.

Referring to FIG. 2, the CNT composite preform 10 prepared by theaforementioned method includes a substrate 102 and a CNT array 110formed thereon. The CNT array 110 includes a number of CNT bundles 114.The CNT bundles 114 includes first ends 112 of the CNTs being adjacentto the substrate 102 and second ends 116 of the CNTs being away from thesubstrate 102. Gaps 118 between the second ends 116 of the two adjacentCNT bundles 114 are bigger than the gaps between the first ends 112thereof.

The CNTs in the CNT composite preform 10 are aligned, with uniquephysical properties, and are easy to handle. The CNT composite preform10 can be applied to a variety of fields, such as electronic materials,thermal materials, optical materials, magnetic materials, catalystmaterials, and so on. The CNT composite is, beneficially, combined withthe metal or polymer composites, e.g., penetration of the metal orpolymer material into the CNT composite perform 10. Due to the size ofthe gaps between the second ends 116 of the CNTs is in the approximaterange from 2 microns to 300 microns, the metal or polymer material caneasily penetrate the CNT array via the aforementioned gaps 118. Thus,better performing composites can be produced.

The following examples are provided by way of illustration to show howthe present CNT composite preform 10 can be prepared, and should not beconstrued as limiting the invention in any way.

Example (1)

Firstly, a substrate 102 is provided 1 centimeter long and 1 centimeterwide; secondly, a CNT array 110 is formed thereon; thirdly, the CNTarray 110 and the substrate 102 are placed in an oxydol solution with amass concentration of 25% and the solution is vacuum treated for 20minutes; fourthly, the CNT array 110 and the substrate 102 are removedfrom the solution; and finally, the CNT array 110 and the substrate 102are dried in a vacuum drying oven to form a CNT composite perform 10.The Scanning Electron Microscope (SEM) image of the second ends 116 ofthe CNTs which are away from the substrate 102 and the cross-section ofthe CNT preform parallel to the CNT array 110 axis and the first ends112 of the CNTs which are near the substrate 102 are shown in FIG. 3,FIG. 4, and FIG. 5 respectively. Gaps 118 between the second ends 116 ofthe two adjacent CNT bundles 114, which are bigger than the gaps betweenthe first ends 112 of the two adjacent CNT bundles 114, can be seen inFIG. 3 to be in an approximate range from 10 to 30 microns.

Example (2)

Firstly, a substrate 102 is provided 1 centimeter long and 1 centimeterwide; secondly, a CNT array 110 is formed thereon; thirdly, the CNTarray 110 and the substrate 102 are placed in water and the solution isvacuum treated for 40 minutes; fourthly, the CNT array 110 and thesubstrate 102 are removed from the solution; and finally, the CNT array110 and the substrate 102 are dried in a vacuum drying oven to form aCNT composite perform 10. The Scanning Electron Microscope (SEM) imageof the second ends 116 of the CNTs is shown in FIG. 6. The sizes of thegaps 118 between the second ends 116 of two adjacent CNT bundles 114, ascan be seen in FIG. 6, are in an approximate range from 15 to 30microns.

Example (3)

Firstly, a substrate 102 is provided 1 centimeter long and 1 centimeterwide; secondly, a CNT array 110 is formed thereon; thirdly, the CNTarray 110 and the substrate 102 are placed in an ethanol solvent and thesolution is vacuum treated for 60 minutes; fourthly, the CNT array 110and the substrate 102 are removed from the solution; and finally, theCNT array 110 and the substrate 102 are dried in a vacuum drying oven toform a CNT composite preform 10. The Scanning Electron Microscope (SEM)image of the second ends 116 of the CNTs is shown in FIG. 7. The sizesof the gaps 118 between the second ends 116 of each two adjacent CNTbundles 114, as can be seen in FIG. 7, are about 300 microns.

Example (4)

Firstly, a substrate 102 is provided 1 centimeter long and 1 centimeterwide; secondly, a CNT array 110 is formed thereon; thirdly, the CNTarray 110 and the substrate 102 are placed in an oxydol solution with amass concentration of 25% and the solution is ultrasonically vibratedfor 30 minutes; fourthly, the CNT array 110 and the substrate 102 areremoved from the solution; and finally, the CNT array 110 and thesubstrate 102 are dried in a vacuum drying oven to form a CNT compositepreform 10. The Scanning Electron Microscope (SEM) image of the secondends 116 of the CNTs is shown in FIG. 8. The sizes of the gaps 118between the second ends 116 of two adjacent CNT bundles 114, as can beseen in FIG. 8, are in an approximate range from 2 to 5 microns.

Example (5)

Firstly, a substrate 102 is provided 1 centimeter long and 1 centimeterwide; secondly, a CNT array 110 is formed thereon; thirdly, the CNTarray 110 and the substrate 102 are placed in water for 40 minutes;fourthly, the CNT array 110 and the substrate 102 are removed from thewater; and finally, the CNT array 110 and the substrate 102 are dried ina vacuum drying oven to form a CNT composite preform 10. The ScanningElectron Microscope (SEM) image of the second ends 116 of the CNTs isshown in FIG. 9. The sizes of the gaps 118 between the second ends 116of two adjacent CNT bundles 114, as can be seen in FIG. 9, are in anapproximate range from 10 to 200 microns.

The CNT composite preform and the method for making the same have thefollowing virtues: first, the gaps between the CNTs away from thesubstrate 102 are penetrable, having a size in the approximate rangefrom 2 microns to 300 microns, thus the CNTs can easily combine with themetal or polymer to form a composite; second, the methods of the presentembodiments have little effect on the properties of the CNT array 110,and the CNTs in the CNT array 110 are aligned; and finally, the methodsare simple, easy to implement, low cost, and consume little time.

It is to be understood that the carbon nanotube array in theabove-described embodiments can be any kind of a plurality of carbonnanotubes formed on the substrate and preferred orientated.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the invention. Variations maybe made to the embodiments without departing from the spirit of theinvention as claimed. The above-described embodiments illustrate thescope of the invention but do not restrict the scope of the invention.

It is also to be understood that the above description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

The invention claimed is:
 1. A method for making a carbon nanotubecomposite preform, the method comprising: providing a substrate; forminga plurality of carbon nanotubes on the substrate; immersing theplurality of carbon nanotubes and the substrate in a solvent for apredetermined time, wherein each of the plurality of carbon nanotubescomprises a first end attached on the substrate, and a second endextending away from the substrate, and a plurality of gas pockets areentrapped between the plurality of carbon nanotubes in the solvent;forming a plurality of honeycomb-shaped gaps between the second ends ofthe plurality of carbon nanotubes by evacuating the plurality of gaspockets entrapped in the plurality of carbon nanotubes from the solventwith an ultrasonic vibration, wherein the plurality of gas pocketsshift-the second ends of the plurality of carbon nanotubes; taking theplurality of carbon nanotubes and the substrate out of the solvent; anddrying the plurality of carbon nanotubes and the substrate.
 2. Themethod as claimed in claim 1, wherein the solvent comprises at least onesubstance selected from the group consisting of water, ethanol, andoxydol solution.
 3. The method as claimed in claim 1, wherein theplurality of gas pockets entrapped in the carbon nanotube compositeperform is evacuated by vacuum treating the plurality of carbonnanotubes and the substrate in the solvent.
 4. The method as claimed inclaim 3, wherein a water-cycle vacuum pump is used in the vacuumtreatments.
 5. The method as claimed in claim 3, wherein the vacuumtreatments facilitate the plurality of gas pockets between adjacentcarbon nanotubes of the plurality of carbon nanotubes migrating to thesecond ends of the plurality of carbon nanotubes.
 6. The method asclaimed in claim 3, wherein the first ends of the plurality of carbonnanotubes are retained in direct contact with the substrate.
 7. Themethod as claimed in claim 6, wherein sizes of the honeycomb-shaped gapsrange from about 2 micrometers to about 300 micrometers.
 8. The methodas claimed in claim 3, wherein the vacuum treatments take about 10minutes to about 60 minutes.
 9. The method as claimed in claim 3,wherein the ultrasonic vibration treatment takes about 10 minutes toabout 60 minutes.
 10. The method as claimed in claim 1, wherein thedrying is conducted in a vacuum drying oven.
 11. The method as claimedin claim 1, wherein the drying is conducted at a temperature in a rangefrom about 40° C. to about 50° C.
 12. The method as claimed in claim 1,wherein the plurality of carbon nanotubes are formed substantiallyperpendicular to the substrate.
 13. The method as claimed in claim 1,the step of forming the plurality of carbon nanotubes further comprisingarranging the plurality of carbon nanotubes in a preferred orientation.14. The method as claimed in claim 1, wherein the plurality of carbonnanotubes are formed by chemical vapor deposition methods or laserablation methods.
 15. A method for making carbon nanotube compositepreform, the method comprising: forming a carbon nanotube array on asubstrate, wherein the carbon nanotube array comprises a plurality ofcarbon nanotubes substantially perpendicular to the substrate; placingthe carbon nanotube array and the substrate in a solvent for apredetermined time, wherein gas is entrapped between the plurality ofcarbon nanotubes in the solvent; evacuating gas between adjacent of theplurality of carbon nanotubes out of the carbon nanotube array byultrasonic vibrating the plurality of carbon nanotubes attached on thesubstrate to form a plurality of honeycomb-shaped gaps between ends ofthe plurality of carbon nanotubes away from the substrate, wherein thegas forms a plurality of gas pockets on the ends of the plurality ofcarbon nanotubes away from the substrate under the vacuum treatment andenlarges gaps between ends of the plurality of carbon nanotubes awayfrom the substrate; drawing the plurality of carbon nanotubes andsubstrate out of the solvent; and drying the plurality of carbonnanotubes and the substrate.
 16. The method as claimed in claim 15,further comprising forming a plurality of honeycomb-shaped gaps bysurface tensions of the plurality of gas pockets.
 17. A method formaking carbon nanotube composite preform, the method comprising: growinga carbon nanotube array on a substrate, wherein the carbon nanotubearray comprises a plurality of carbon nanotubes substantiallyperpendicular to the substrate, and the carbon nanotube array comprisesa first end adjacent to the substrate, and a second end extends awayfrom the substrate; immersing the carbon nanotube array and thesubstrate in a solvent for a predetermined time, wherein gas isentrapped between the plurality of carbon nanotubes in the solvent;evacuating gas between adjacent of the plurality of carbon nanotubes outof the carbon nanotube array from the first end to the second end byultrasonic vibrating the plurality of carbon nanotubes fixed on thesubstrate, and enlarging gaps between the plurality of carbon nanotubesin the second end; drawing the plurality of carbon nanotubes andsubstrate out of the solvent; and drying the plurality of carbonnanotubes and the substrate to leave the plurality of carbon nanotubeson the substrate.
 18. The method of claim 17, wherein the first end ofthe carbon nanotube array is attached on the substrate in the step ofevacuating the gas, and gaps between two adjacent second ends of thecarbon nanotube array is smaller than gaps between two adjacent firstends of the carbon nanotube array.